1. Field of the Invention
The present invention relates to a conveyance apparatus using movable bodies, which includes a rail device and movable bodies capable of moving along a fixed path by being supported and guided by this rail device, each movable body having a main body provided with a supporting unit for an item to be conveyed and connected with guided devices that are supported and guided by the rail device at positions corresponding to the front and rear ends of the supporting unit.
2. Description of the Related Art
Conventionally, the composition illustrated in Japanese Unexamined Patent Publication No. 7-25441 has been proposed as a conveyance apparatus of this kind. In other words, the main body of a movable body capable of moving along a fixed path by being supported and guided on rails is formed by three frame bodies which are connected in a relatively rotatable fashion by means of connecting devices. The frame bodies each comprise a rectangular shaped body which is elongated in the direction of the fixed path, and the side faces thereof are formed as passive surfaces. The middle frame body is provided with a conveyed item supporting unit and guided devices which are supported and guided by the rails, and the front and rear side frame bodies are each provided with a guided device which is supported and guided by the rails.
In this case, all (four) of the guided devices are formed in a trolley structure including vertical pins installed rotatably on the respective end frame members provided in the frame body, a trolley main body connected rotatably to the lower ends of these vertical pins by means of lateral pins, total four supported rollers installed on both sides of the trolley main body in front and rear pairs, and a total of four guided rollers installed on the upper and lower sides of the trolley main body in front and rear pairs.
Idle wheels are installed on the lower side of the item supporting unit, and a pair of guide rails which support these idle wheels from below are provided along a fixed path. These rails have a channel shape, and are provided as a right and left-hand pair of rails, with open sections of the respective rails mutually facing each other. A guide frame body for guiding an upper guided roller is fixed to the upper edge section of the open section of each rail, and a guide frame body for guiding a lower guided roller is fixed to the lower edge section.
If a conventional structure of this kind is adopted, the movable body is moved along a fixed path by means of the group of supported rollers of the respective guided devices being supported and guided by the rails, and by means of the group of guided rollers being guided by the guide frame body. Moreover, the weight of the item supporting unit is supported by means of the idle wheels being supported and guided by the guide rails.
However, according to the conventional composition described above, the groups of idle wheels are disposed in a fixed state in an uniform posture (orientation) with respect to the item supporting unit. Therefore, in a curved path which turns in the right or leftward direction in a plan view, the central axis linking the right and left-hand idle wheels is orientated in parallel with the radius of the curve. In other words, the group of idle wheels are orientated in a direction that is inclined with respect to the curved path of the guide rails, and therefore, there may arise such cases that the group of idle wheels produce frictional rotation, accompanied by slipping (friction resistance), which causes movement to be hard to be smooth due to the frictional rotation occurring at a plurality of positions. Therefore, the item supporting unit may be supported and guided along the guide rails whilst toppling or catching with respect to the guide rails, and therefore the movement of the movable body along the curved path cannot be performed smoothly. Further, the composition and disposition (configuration) of the guide rails in the curved path differs from that in a linear path, and therefore the installation of the guide rails in the curved path becomes complicated and expensive.
According to the conventional composition described above, since the guided devices are connected by inserting the lower ends of vertical pins bearing weight into the trolley main body, such a composition is obtained that is liable to produce toppling in the coupling sections. Therefore, especially when a large (wide or high) item having an unbalanced load is being conveyed, the inclination of the item supporting unit, in other words, the conveyed item, will increase, and there is a risk that problems will occur in the stability of the conveyance operation. In order to resolve such problems, it is necessary to adopt large and expensive guided devices which have the strength to support large loads. Accordingly, the guided devices become expensive, that is, the overall device becomes expensive.
Moreover, according to the conventional composition described above, the same structure is adopted for all of the guided devices, with the aim of achieving standardization of components. In this case, however, the same composition as of the middle section guided devices is adopted, which is strong enough to bear high loads and is expensive, for the guided devices at the front and rear ends where the load is small, so that the overall device becomes expensive. Moreover, since the front and rear pairs of guided rollers of the guided devices are guided by the guide frame body, the guided devices rotate relatively about the vertical pins with respect to the longitudinal direction of the frame body, in a curved path which turns in the right or leftward direction in plan view. In this case, all of the total of four supported rollers in the guided devices in the end sections, in particular, become orientated in parallel to the tangent to the curve in the region of the vertical pins, in other words, the supported rollers are orientated in a direction that diverges from the direction of movement of the frame body. Accordingly, the group of supported rollers perform frictional rotation, accompanied by slipping (frictional resistance), and hence there may be such cases that the movement cannot be performed smoothly due to the frictional rotation at these four points. Therefore, the guided devices may topple or catch with respect to the guide rails while being guided along the rails, and hence the movement of the movable body along a curved path section may not be performed smoothly.